When a typhoon arrives, a load on a wind turbine is increased. In a case that the yaw load is not reduced timely, the wind turbine even the entire wind farm is apt to be damaged.
A yaw system of a wind turbine may generally include a hydraulic brake mechanism, an electronic brake mechanism, and a yaw drive mechanism.
In a case that there is a certain wind direction deviation angle between a wind direction and an axis of a nacelle of the wind turbine, which lasts for a period of time, the axis of the nacelle is adjusted to a direction consistent with the wind direction by the yaw drive mechanism, thereby the nacelle is downwind oriented. In yaw, the electronic brake mechanism is released first, and the hydraulic brake mechanism is in a semi-released state, so as to set a sufficient damping and maintain sufficient stability of the nacelle during yaw. The yaw drive mechanism may include a yaw motor. The yaw motor drives a pinion and in turn drives the entire nacelle to rotate along a yaw bearing, achieving yaw of the nacelle.
In a case that the yaw motor is stopped, the hydraulic brake mechanism is in a braking state, and fixes the nacelle to a corresponding position. In a case that the nacelle yaws to a certain angle, a generator cable that extends from the nacelle to the bottom of the tower is in a winding state. In such case, the wind turbine performs a cable-unwinding process. Namely, the wind turbine yaws oppositely to a direction of the cable winding, so as to unwind the cable. The hydraulic brake mechanism is in a fully released state in order to unwind the cable quickly.
As described above, cooperation of the hydraulic brake mechanism, the electronic brake mechanism, and the yaw drive mechanism is required to implement the yaw control of the wind turbine. In a case that the yaw system fails, it is difficult to perform an effective yaw control on the wind turbine.